Radio communication apparatus and method for preventing hidden terminals from interrupting communications

ABSTRACT

A radio communication method for transmitting and receiving data between a first terminal and a second terminal comprises the following two steps. A step of establishing a connection between the first terminal and the second terminal when the first terminal and the second terminal have detected that a signal has not been transmitted on a predetermined channel, and the other step of starting data communications between the first terminal and the second terminal which have established the connection, and transmitting the predetermined signal on the predetermined channel from both the first terminal and the second terminal throughout the data communications.

This is a division of U.S. Ser. No. 08/404,047, filed on Mar. 14, 1995,for a RADIO COMMUNICATION APPARATUS AND METHOD FOR PREVENTING HIDDENTERMINALS FROM INTERRUPTING COMMUNICATIONS, U.S. Pat. No. 5,754,947.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an apparatus and method for radiocommunication in a radio network, and particularly to such an apparatusand method applicable to a distributed environment, i.e. a network whichhas a distributed topology.

(2) Description of the Related Art

Radio networks with the use of radio wave or infrared light have been ingreat demand these days because they require no communication cables.Radio terminals can intercommunicate from any site within theircommunication ranges, and be used on the move when they are reduced toportable.

However, radio networks often suffer from so called "Hidden TerminalProblem" which does not affect wired networks and is caused by a radioterminal outside their communication ranges.

FIG. 1 is an illustration to be used to explain a Hidden TerminalProblem (hereinafter HTP).

A, B, and C are radio terminals, and the circles represent respectivecommunication ranges. When terminal A is communicating with terminal B,terminal C is getting no signal from terminal A. Consequently, terminalC might start to communicate with terminal B, without knowing thecommunications between terminals A and B. If terminal B is thuscommunicated from both terminals A and C, the communication carried outso far between terminals A and B ends up in vain. Thus, the occurrenceof HTP requires retransmission, reducing data transmission throughput inradio networks.

In order to solve the HTP, various radio network communication schemeshave been proposed as follows.

<CSMA/CA+Ack>

A communication scheme called CSMA/CA+Ack (Carrier Sense Multiple Accesswith Collision Avoidance plus Acknowledgement) has been proposed by W.Diepstraten in "A Distributed Access Protocol Proposal Supporting TimeBounded Service" (IEEE Working Group Paper 802.11-93/70).

Although this scheme is not directly concerned with the solution of HTP,it is a basic communication scheme in networks and referred to later inthe explanation of communication schemes.

Generally, multiple accesses in a network can be realized based on a MAC(Medium Access Control) layer protocol. The CSMA/CA+Ack is a MAC layerprotocol based on CSMA/CA which is widely used as a MAC layer protocolin a radio network. The CSMA/CA+Ack has a function for acknowledgementand retransmission of frames at a MAC layer level, in addition to thefunctions of CSMA/CA. The CSMA/CA is more suitable to radiocommunications than CSMA/CD (CSMA with Collision Detection) which iswidely used as the MAC layer protocol in cable networks.

According to the CSMA/CA+Ack, a first terminal which is ready totransmit data makes sure that the transmission path has no signal for apredetermined gap time period, and then starts the data transmission inframes to a second terminal. The second terminal, which has received theframes returns a confirming frame to the first terminal in order toreport the successful reception of the frames, after having made surethat the transmission path has no signal for a predetermined gap timeperiod.

Although the use of the confirming frames has improved the reliabilityof the data transmission, this scheme presupposes that a signaltransmitted by any of terminals is distributed to all the terminals inthe network, which does not insist on solving the HTP.

<K. Biba>

K. Biba has proposed a scheme of solving HTP in "A hybrid Wireless MACProtocol Supporting Asynchronous and Synchronous MSDU Delivery Service"(IEEE Working Group Paper 802.11-91/92). In order to avoid HTP, atransmitting terminal and a receiving terminal establishes a connectionevery time a frame is transmitted, and informs the other terminals of atime period during which the transmission path is occupied inestablishing a connection.

According to this scheme, a transmitting terminal sends an RTS (requestto send) frame prior to a data transmission, and a receiving terminalreturns a CTS (Clear to Send) frame to report the reception of the RTSframe. Then, the transmitting terminal sends data in frames, and thereceiving terminal returns an ACK frame to report the receipt of theframes. An RTS frame carries the length of data to be transmitted, and aCTS frame carries the length of data to be received. Prior to thetransmission of RTS frames and CTS frames, the condition of thetransmission path is checked with CSMA. The terminals other than thedestination of an RTS frame check the length of the data carried in theframe and refrain from accessing the transmission path until thetransmission and acknowledgement of the data is completed. In the samemanner, the terminals other than the destination of a CTS frame do notaccess the transmission path until the transmission and acknowledgementof the data is completed. This is how HTP is solved in this system.

However, a connection must be established per frame, so that theefficiency of data transmission is decreased when large data beingdivided into a plurality of frames are transmitted.

For another problem, the transmission of an RTS (or CTS) frame may besometimes unsuccessful because of a collision. In that case, a terminalwhich successfully received the RTS (or CTS) frame must be deprived ofthe access to the transmission path in vain for the time periodcorresponding to the unexecuted data transmission.

For further another problem, there is a possibility that a terminalwhich moved into the transmission range of the receiving terminal startsanother data transmission without knowing the preceding datatransmission. Thus, HTP resulting from a terminal's movement cannot besolved.

<Japanese Laid-open Patent Application No. 5-260051>

The scheme proposed in Japanese Laid-open Patent Application No.5-260051 is used in a system composed of a plurality of terminals, and abase station which communicates with all the terminals. An availablefrequency band is divided into a message channel, an up link channel,and a down link channel.

A terminal which is ready to transmit data checks the presence orabsence of a channel tone, and in the case of its absence, transmits achannel tone on the up link channel. Detecting the channel tone, thebase station transmits the same channel tone on the down link channel.Detecting the return of the channel tone, the terminal starts datatransmission.

This scheme requires the base station to solve HTP, so that in case thatthe base station is out of order, all the terminals in the networkbecomes unable to communicate, deteriorating the reliability of theentire network.

<U.S. Pat. No. 4,409,687>

The communication scheme disclosed in U.S. Pat. No. 4,409,687 can use aplurality of channels assigned to different frequencies, and is used ina system composed of a plurality of terminals and a base station. Aterminal in the transmission mode scans all the channels prior to a datatransmission, and if a channel in the idle state is found, the terminaltransmits a busy tone on the channel and further transmits apredetermined group tone. Receiving the busy tone from the terminal, thebase station transmits the busy tone on the channel, and further repeatsthe group tone. A terminal in the reception mode scans all the channels,and establishes a connection with the transmitter in response to thereception of the predetermined group tone.

This scheme can solve HTP; however, it still requires a base station(repeater), and as a result this system suffers from the same problemsas the above mentioned Japanese Laid-open Patent Application No.5-260051.

<U.S. Pat. Nos. 4,360,927 and 4,658,435>

U.S. Pat. Nos. 4,360,927 and 4,658,435 have also disclose communicationschemes capable of solving the HTP and of using a plurality of channels;however, these schemes require a base station, suffering the sameproblems as mentioned above.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an apparatus andmethod of radio communication capable of avoiding HTP in a radio networkand applicable to a distributed environment having no base station,thereby realizing a high reliability and high transmission efficiency.

The object can be achieved by a radio communication method fortransmitting and receiving data between a first terminal and a secondterminal. The method comprises the following steps:

establishing a connection between the first terminal and the secondterminal when the first terminal and the second terminal have detectedthat a signal has not been transmitted on a predetermined channel; and

starting data communications between the first terminal and the secondterminal which have established the connection, and transmitting apredetermined signal on the predetermined channel from both the firstterminal and the second terminal throughout the data communications.

The connection establishment step may comprise the following sub steps:

detecting a presence or absence of the signal transmitted on thepredetermined channel, by the first terminal;

transmitting a first control signal from the first terminal to thesecond terminal in a case where the absence of the signal transmitted onthe predetermined channel has been detected by the first terminal;

detecting a presence or absence of the signal transmitted on thepredetermined channel, by the second terminal, when the second terminalhas received the first control signal;

transmitting a second control signal from the second terminal to thefirst terminal in a case where the absence of the signal transmitted onthe predetermined channel has been detected by the second terminal; and

receiving the second control signal by the first terminal.

Each of the first terminal and the second terminal may be assigned acontrol channel provided for connection establishment and a data channelprovided for data transmission, and the predetermined channel may be thecontrol channel.

According to the above construction, both a transmitting terminal and areceiving terminal transmit a busy tone on a control channel while theyare in process of data communication. Another terminal which is ready totransmit data is supposed to check before data transmission that thereis no busy tone transmitted, so that the terminal can startcommunication only when no terminal which is inside the checkingterminal's communication range is in a communication process. As aresult, HTP can be prevented.

Furthermore, the HTP is prevented by transmitting a busy tone, so that ahighly reliable radio network can be constructed in a distributedenvironment which is dispensable with a base station.

Each of the first terminal and the second terminal may be assigned adata channel provided for connection establishment and data transmissionand a control channel, and the predetermined channel may be the controlchannel.

According to the above-mentioned construction, the control channel isused only for the transmission of busy tones. Consequently, the bandwidth for the control channel can be narrower, thereby making a good useof frequency band width.

The connection establishment step may further comprise the sub step ofstarting a transmission of the predetermined signal on the controlchannel from the second terminal, at a predetermined time point after acompletion of the sub step of detecting the presence or absence of thesignal transmitted on the control channel by the second terminal.

The connection establishment step may further comprise the sub step oftransmitting the predetermined signal on the control channel from thefirst terminal concurrently with a transmission of the first controlsignal from the first terminal.

According to the above-mentioned construction, busy tones aretransmitted on the control channel also in the connection establishmentstep. Consequently, data communication in a connection establishmentstep is less affected by another terminal, establishing a connection ina shorter time.

The object can be achieved by a radio communication apparatus fortransmitting and receiving data to and from a desired radiocommunication apparatus.

The radio communication apparatus comprises the following units:

a connection establishment unit for detecting a presence or absence of asignal transmitted on a predetermined channel, and for establishing aconnection with the desired radio communication apparatus when theabsence of the signal transmitted on the predetermined channel has beendetected;

a data communication unit for starting data communications with thedesired radio communication apparatus, responding to the connectionestablishment; and

a signal transmission unit for continuing a transmission of apredetermined signal on the predetermined channel from the radiocommunication apparatus and the desired radio communication apparatusthroughout the data communications.

The connection establishment unit may comprise the following units:

a detection unit for detecting a presence or absence of the signaltransmitted on the predetermined channel;

a control signal transmission unit for selectively transmitting one of afirst control signal and a second control signal;

a control signal reception unit for receiving the first control signaland the second control signal; and

a control unit for controlling the control signal transmission unit totransmit the first control signal when the detection unit has detectedthe absence of the signal transmitted on the predetermined channel in acase where the radio communication apparatus is a transmitting terminal,and for, in a case where the radio communication apparatus is areceiving terminal, controlling the control signal transmission unit totransmit the second control signal to the desired radio communicationapparatus after the first control signal has been received by thecontrol signal reception unit and the signal has been detected to beabsent on the predetermined channel by the detection unit.

The control signal transmission unit may transmit the first controlsignal and the second control signal on a control channel, the datacommunication unit may perform the data communications on a data channelprovided apart from the control channel, and the predetermined channelmay be the control channel.

The control signal transmission unit may transmit the first controlsignal and the second control signal on the data channel, the datacommunication unit may perform data communications on the data channel,and the predetermined channel may be a control channel provided apartfrom the data channel.

The control unit may further comprise the following units:

a receiving terminal signal transmission control unit for controllingthe signal transmission unit to start a transmission of thepredetermined signal on the control channel at a predetermined timepoint after a detection of the absence of the signal transmitted on thecontrol channel and before a commencement of the data communications, ina case the radio communication apparatus has received the first controlsignal.

The control unit may further comprise the following units:

a transmitting terminal signal transmission control unit for controllingthe signal transmission unit to continue the transmission of thepredetermined signal on the control channel while the control signaltransmission unit is transmitting the first control signal.

According to these constructions, the same effects as the abovementioned method can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings which illustrate a specificembodiment of the invention. In the drawings:

FIG. 1 is an illustration to be used to explain a HTP.

FIG. 2 shows the types of frames transmitted and received between twoterminals in the first embodiment of the present invention.

FIGS. 3A-3F show the formats of these frames of FIG. 2.

FIG. 4 shows the construction of the radio communication apparatus ofthe first embodiment.

FIG. 5 shows the detailed construction of the MAC unit 3 of the firstembodiment.

FIGS. 6A and 6B show the constructions of the modem 4 for the datachannel and the modem 5 for the busy tone channel respectively.

FIG. 7 is a flowchart showing the overall operations of the radiocommunication apparatus of the first embodiment.

FIG. 8 is a flowchart showing the data transmission operation of theradio communication apparatus of the first embodiment.

FIG. 9 is a flowchart showing the data reception operation of the radiocommunication apparatus of the first embodiment.

FIG. 10 is a graph showing the results of a numerical simulation of thethroughput property of the radio communication apparatus of the firstembodiment.

FIG. 11 is a table showing the average path loss in the case that HTP ispresent, which is used to simulate the throughput property of the radiocommunication apparatus of the first embodiment.

FIG. 12 is a block diagram showing the detailed construction of the MACunit 3 of the second embodiment.

FIG. 13 is a block diagram showing the construction of the modem 5 forthe busy tone channel of the radio communication apparatus of the secondembodiment.

FIG. 14 is a flowchart showing the overall operation of the radiocommunication apparatus of the second embodiment.

FIG. 15 is a flowchart showing the data transmission operation of theradio communication apparatus of the second embodiment.

FIG. 16 is a flowchart showing the data reception operation of the radiocommunication apparatus of the second embodiment.

FIG. 17 is a flowchart depicting the RCON frame transmission operationof the radio communication apparatus of the third embodiment.

FIG. 18 is a flowchart depicting a CCON frame transmission operation ofthe radio communication apparatus of the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1>

(The Frame Format)

First of all, frames to be transmitted to/from the radio communicationapparatus of the first embodiment of the present invention is explainedas follows.

FIG. 2 shows a frame transmission between two terminals. Here, a "frame"represent a minimum unit of information to be transmitted to/from theradio communication apparatus. The frames are classified into fourtypes: an RCON (Request Connection) frame and a CCON (ConfirmConnection) frame which are used for establishing a connection, and aDATA frame and an ACK (Acknowledgement) frame which are used fortransmitting data.

As shown in FIG. 2, a transmitting terminal transmits an RCON frame, anda receiving terminal returns a CCON frame, thereby establishing aconnection. In response to the establishment of the connection, thetransmitting terminal transmits a DATA frame, and the receiving terminalreturns an ACK frame, thereby completing the transmission of data forone frame. The transmission of the DATA frame and the ACK frame arerepeated until all the necessary data are transmitted.

FIGS. 3A-3F show the formats of these frames. FIG. 3A shows componentsthat all the frames commonly have, namely, preamble, start delimiter,common header, CRC (Cyclic Redundancy Check) code, and end delimiter.The DATA frame further has a data unit. The CRC code indicatesinformation necessary for detecting bit errors.

FIG. 3B show the format of a common header, which consists of a typefield, a destination address field, a source address field, and asequence number field.

The type field carries the type of its frame. The most significant bitof the type field is called EOP (End of Packet) bit. In the case of RCONand CCON frames, the EOP bit always has a 0 value. In the case of DATAframes, the EOP bit is set to 1 value only when the frame is the lastframe constructing a data packet sent from an upper layer protocol, andotherwise it is set to a 0 value. The EOP bit of an ACK frame issupposed to be equal to the EOP bit of the DATA frame which has beenjust confirmed.

The destination field carries a destination address.

The source address field carries the address of the radio communicationapparatus, which tries to send the frame.

The sequence number field in an RCON frame carries the sequence numberof the first DATA frame to be transmitted on a connection established bythe use of the RCON frame. The sequence number field in a CCON framecarries the same sequence number as in the sequence number field in theRCON frame that is confirmed by the CCON frame. The sequence numberfield in a DATA frame carries a sequence number which indicates theorder of the frame in the sequence. The sequence number field of an ACKframe carries the sequence number of the DATA frame that is confirmed bythe ACK frame. In the case of the radio communication apparatus of thepresent embodiment, the sequence number has a 0 value when it is booted,and is incremented by one, every time the apparatus transmits a new DATAframe, which is not for retransmission. If a value 1 is added to thesequence number in the case that the sequence number is the maximumvalue to be obtained with the bit length of the sequence number field,the value becomes 0.

FIG. 3C shows the format of an RCON frame. An RCON frame does not have adata unit, its type field carries a value which is identified as an RCONframe, and its EOP bit always has a 0 value. The sequence number fieldcarries the sequence number of the next coming DATA frame.

FIG. 3D shows the format of a CCON frame. A CCON frame does not have adata unit, its type field carries a value which is identified as a CCONframe, and its EOP bit always has a 0 value. The sequence number fieldcarries the sequence number written in the RCON frame to be confirmed bythe CCON frame.

FIG. 3E shows the format of a DATA frame. A DATA frame has a data unit,and its type field carries a value which is identified as a DATA frame.The EOP bit is set to 1 in the case that the DATA frame is the lastframe constructing a data packet sent from an upper layer protocol, andotherwise it is set to 0. The sequence number field carries the sequencenumbers of the DATA frame, which represents the order of the DATA frame.

FIG. 3F shows the format of an ACK frame. An ACK frame does not have adata unit, and its type field carries a value which is identified as anACK frame. Its EOP bit is supposed to be equal to the EOP bit of theDATA frame to be confirmed by the ACK frame. The sequence number fieldcarries the same sequence number written in the DATA frame to beconfirmed by the ACK frame.

(The Overall Construction of the Radio Communication Apparatus)

FIG. 4 shows the construction of the radio communication apparatus ofthe present embodiment, composed of a CPU 0, a memory 1, a DMAcontroller 2, an MAC unit 3, a modem 4 for a data channel, a modem 5 fora busy tone channel, a bus 6, a duplexer 7, and an antenna 8.

The CPU 0 is in charge of data communication with the memory 1, framegeneration, connection management, MAC unit 3 operation management,communication with users, and the entire apparatus management.

The memory 1 stores data to be transmitted and received data, framesgenerated or received by the CPU 0, and connection control tablesgenerated by the CPU 0.

The DMA controller 2 performs data communications between the MAC unit 3and the memory 1.

The MAC unit 3 is in charge of data format conversion between the memory1 and the modems 4 and 5, frame border recognition, attachment anddetachment of preambles, start delimiters, and end delimiters,generation and examination of CRC codes, and identification of receivedframe addresses.

The modem 4 for the data channel modulates a carrier wave having afrequency for the data channel with data sent from the MAC unit 3,thereby transmitting the modulated signal to the duplexer 7, and alsodetects data from a signal sent from the duplexer 7 to transmit them tothe MAC unit 3.

The modem 5 for the busy tone channel modulates a carrier wave having afrequency for the busy tone channel with data sent from the MAC unit 3,thereby transmitting the modulated signal to the duplexer 7, and alsodetects data from a signal sent from the duplexer 7 to transmit them tothe MAC unit 3. In the present embodiment, the radio waves havingdifferent frequency bands from each other are respectively assigned tothe data channel and the busy tone channel.

The bus 6 is a medium for the exchange of control signals among thecomponents of the radio communication apparatus, and for the datatransmission between the memory 1 and the DMA controller 2.

The duplexer 7 distributes signals sent from the antenna 8 to the modem4 for the data channel and to the modem 5 for the busy tone channel,depending on their frequency bands. The duplexer 7 also combines thesignals sent from both modems 4 and 5, thereby forwarding them to theantenna 8.

The antenna 8 transmits and receives radio signals.

(The Construction of MAC Unit 3)

FIG. 5 shows the detailed construction of the MAC unit 3 which iscomposed of a MAC control unit 30, a FIFO 31 for reception, a FIFO 32for transmission, a busy tone reception unit 33, a busy tonetransmission unit 34, a data reception unit 35, a data transmission unit36, and a busy tone determination unit 37.

The MAC control unit 30 controls each component of the MAC unit 3 andexchanges information with the CPU 0 via the bus 6, and further informsthe modems 4 and 5 the timing for switching between the reception andtransmission of frames via the signal conductors 302 and 303.

The FIFO 31 for reception and FIFO 32 for transmission are buffers fortransmitting data to and receiving data from the DMA controller 2respectively.

The busy tone reception unit 33 detects a frame head by detecting astart delimiter from a bit stream received through the modem 5 for thebusy tone channel, and checks the destination address to determinewhether the frame is destined for the apparatus. If it is destined forthe apparatus, the busy tone reception unit 33 reports this to the MACcontrol unit 30, and transfers the received frame to the FIFO 31 forreception. The received frame is further transferred to the memory 1 bythe DMA controller 2.

The busy tone transmission unit 34 transmits a frame sent from the FIF032 for transmission under the direction of the MAC control unit 30through the modem 5 for the busy tone channel.

The data reception unit 35 detects a frame head by detecting a startdelimiter from a bit stream received through the modem 4 for the datachannel, and checks the destination address to determine whether theframe is destined for the apparatus. If it is destined for theapparatus, the data reception unit 35 reports it to the MAC control unit30, and deletes the preamble, start delimiter, CRC code, and enddelimiter from the received frame. Then, the data reception unit 35transfers the rest of the received frame to the FIFO 31 for reception.The contents of the FIFO 31 is transferred to the memory 1 by the DMAcontroller 2.

The data transmission unit 36 generates a frame by adding the preamble,start delimiter, CRC code, and end delimiter to the contents of the FIFO32 under the direction of the MAC control unit 30, and transmits theframe to the modem 4, thereby transmitting the frame on the datachannel.

The data transmission from the memory 1 to the FIFO 32 is performed bythe MAC controller 2.

The busy tone determination unit 37 observes the strength of a signal onthe busy tone channel received by the modem 5 and determines whether thesignal strength is beyond a predetermined one. The observed result isreported to the MAC control unit 30 via the signal conductor 304. TheMAC control unit 30, prior to the transmission of an RCON frame or aCCON frame, performs a gap detection with a signal sent through thesignal conductor 304, to detect whether the busy tone channel is freefrom a signal having more strength than determined for over apredetermined time period (gap time).

(The Construction of Modems 4 and 5)

FIG. 6A shows the construction of the modem 4 for the data channel.

The Rx/Tx switch 40 switches between the transmission mode and thereception mode under the direction of the MAC control unit 30.

Under the reception mode, signals from the duplexer 7 are sent to thedemodulator 44 through the receiver 43, and further sent to the datareception unit 35 after detection, decision, and clock recovery havebeen applied.

Under the transmission mode, the modulator 42 modulates a carrier wavefor the data channel by means of a bit stream sent from the datatransmission unit 36, thereby generating modulated signals. Themodulated signals are sent to the duplexer 7 through the transmitter 41.

The Rx/Tx switch 40, the transmitter 41, and the receiver 43, which areconnected with the MAC control unit 30 through a signal conductor 302,operate under the direction of the MAC control unit 30.

FIG. 6B shows the construction of the modem 5 for the busy tone channel,which is similar to the construction of the modem 4 shown in FIG. 6A.The receiver 53 and the busy tone determination unit 37 are connected toeach other via a signal conductor 301, which informs the strength of asignal received on the busy. tone channel. The busy tone determinationunit 37 determines whether there is a signal having more strength thanpredetermined by means of the signal conductor 301, then reports theresult to the MAC control unit 30.

(Overall Operations of the Radio Communication Apparatus)

FIG. 7 is a flowchart showing overall operations of the radiocommunication apparatus of the present embodiment. More detailedoperations will be described later with reference to FIGS. 8 and 9.

Having received an RCON frame destined for itself on the busy tonechannel (step R), the radio communication apparatus performs a datareception subroutine, and returns to the step R when the data receptionhas been completed.

Not having received an RCON destined for itself (step R), the radiocommunication apparatus determines whether there are data to betransmitted in the memory 1 (step S). When the presence of such data hasbeen determined, the apparatus performs a data transmission subroutine,and returns to the step R. In contrast, when the absence of such datahas been determined, the apparatus directly returns to the step R.

As will be described below, when an RCON frame destined for theapparatus has been received on the busy tone channel at an early stageof a connection establishing process, a data reception process hasprecedence over the data transmission process.

(Data Transmission Operations)

Detailed operations for data transmission of the radio communicationapparatus are as follows.

FIG. 8 is a flowchart showing data transmission operations of theapparatus. When data to be transmitted have been stored to the memory 1by means of an upper layer application (step S), the CPU 0 generates aconnection control table and stores it to a predetermined area in thememory 1 (step S01). The connection control table includes thedestination address for the data, the current value of the sequencenumber (hereinafter CSEQ), the maximum frame length inherent to the datachannel to be used, the number of times to retransmit an RCON frame, thenumber of times to retransmit a DATA frame, and a connection state.

In step S01, the address of the receiving station is set to thedestination address of the data to be transmitted, and CSEQ is set to avalue to be obtained by adding 1 to the sequence number of thelatest-transmitted DATA frame (hereinafter LSEQ). The numbers of timesto retransmit an RCON frame and a DATA frame are both set to 0. Theconnection state is set to an RCON transmission wait state.

In data transmission, the CPU 0 stores CSEQ to a predetermined area inthe memory 1 as LSEQ, every time a new DATA frame is transmitted, whichis not for retransmission.

Then, the CPU 0 generates a common header of the RCON frame (hereinafterRCON header), and stores it to a predetermined area in the memory 1(step S02). The parts other than the common header, namely, preamble,start delimiter, CRC code, end delimiter are generated in the busy tonetransmission unit 34 and added to the RCON frame when it is transmitted.

The type field in the RCON header carries an identification of the typeof RCON. The destination address field and the sequence number fieldrespectively carry the destination address and CSEQ of the connectioncontrol table. The source address field carries the address of theapparatus.

The CPU 0 stores the generated RCON header to the FIFO 32 fortransmission (step S03). To be more specific, the CPU 0 informs the DMAcontroller 2.of the leading address and the length of the RCON header inthe memory 1. The DMA controller 2 serially stores data for the informedlength starting from the informed address to the FIFO 32. The CPU 0informs the MAC control unit 30 of the start of the data transmission aswell as directing it to store the RCON header. The generated RCON headeris held in the memory 1 until it is confirmed by the CCON frame.

The MAC control unit 30 starts to observe the conditions of the busytone channel in accordance with the signal to be sent from the busy tonede-termination unit 37 to the signal conductor 304 (step S04). When thesignal on the signal conductor 301 has less strength than thepredetermined one, the busy tone determination unit 37 determines theabsence of an effective signal on the busy tone channel, and transmits alow level signal through the signal conductor 304 to inform the MACcontrol unit 30 of the determination. In accordance with this, the MACcontrol unit 30 regards the absence of the effective signal for thepredetermined gap time as the detection of a gap on the busy tonechannel.

In response to the detection of the gap (step S05), the MAC control unit30 switches the Rx/Tx switch 50 in the modem 5 to the transmitter, bysending a signal to the signal conductor 303, thereby setting the modem5 to the transmitting mode. This signal is also used to initiate thetransmitter 51. The MAC control unit 30 directs the busy tonetransmission unit 34 and the FIFO 32 to transmit a frame. The busy tonetransmission unit 34 generates a data stream including a preamble and astart delimiter at the head of an RCON header, and converts the datastream into a bit stream for the transmission path, and starts totransmit it to the modulator 52 of the modem 5. When the RCON header inthe FIFO 32 has been all transmitted, the busy tone transmission unit 34adds already calculated CRC code and the end delimiter to the end of theRCON header, converts it into a bit stream for the transmission path,and transmits it to the modulator 52. The modulator 52 modulates acarrier wave for the transmitted bit stream, and transmits the bitstream onto the busy tone channel through the transmitter 51, duplexer7, and antenna 8 (step S06).

When the transmission of the end delimiter of the RCON frame to themodulator 52 has been completed, the busy tone transmission unit 34informs the MAC control unit 30 of the completion of the transmission.The MAC control unit 30 waits until the modem 5 completes thetransmission of the RCON frame, then switches the Rx/Tx switch 50 to thereceiver, by sending a signal to the signal conductor 303. As a result,the modem 5 for the busy tone channel is set to the reception mode. Thissignal is also used to initiate the receiver 53. Then, the MAC controlunit 30 informs the CPU 0 of the completion of the RCON frametransmission. The CPU 0 changes the connection state of the connectioncontrol table in the memory 1 to the CCON reception wait state (StepS07). Then, the CPU 0 starts the CCON wait timer with 0 as the initialvalue (step S08).

When a signal on the busy tone channel is received by the receiver 53 inthe modem 5 and sent to the busy tone reception unit 33 through thedemodulator 54 in the form of a bit stream, the busy tone reception unit33 finds out the bit pattern of the start delimiter from the bit stream,and regards the bits following the start delimiter as a frame. Judgingthe frame to be destined for the apparatus, the busy tone reception unit33 reports it to the MAC control unit 30, and converts the receivedframe from the bit stream for the transmission path into a data streamuntil the end delimiter is detected, storing them to the FIFO 31 forreception. The end delimiter is not stored to the FIFO 31. The busy tonereception unit 33 examines the CRC of the frame. Prior to the framestorage to the FIFO 31, the MAC control unit 30 sends a control signalto the FIFO 31 to enable the writing of data from the busy tonereception unit 33.

The DMA controller 2 transfers frames stored in the FIFO 31 to thememory 1. To be more specific, the DMA controller 2, which holds theleading address and length of the preserved area on the memory 1, startsto transfer the contents of the FIFO 31 from the site of the leadingaddress, and interrupts in the CPU 0 when all the contents of the FIFO31 have been stored or when the stored data has reached the length. Inthis embodiment, the preserved area in the memory 1 is supposed to belarge enough to store at least one frame including a DATA frame. Undersuch assumption, the DMA controller starts an interruption when all thecontents of the FIFO 31 have been stored in the memory 1.

Having detected a CRC error in the process of CRC examination, the busytone reception unit 33 reports it to the MAC control unit 30. The MACcontrol unit 30 makes an interruption to inform the CPU 0 of the CRCerror. The CPU 0 directs the DMA controller 2 to transmit next data tothe very area in the memory 1 where the frame with the CRC error isstored, thereby eliminating the frame.

Receiving the interruption which informs the completion of the framestorage, and not receiving the interruption which informs the detectionof the CRC error, the CPU 0 checks the type field of the frame stored inthe memory 1. When the type is CCON (step S09), the contents of thesource address field and the sequence number field are compared with thecontents of the connection control table. When they agree (step S10),the CPUO stops the CCON wait timer (step S11), and deletes the RCONheader held in the memory 1 for retransmission.

Then, the CPU 0 directs the MAC control unit 30 to start busy tonetransmission. The MAC control unit 30 sends a signal to the signalconductor 303 to switch the Rx/Tx switch 50 in the modem 5 to thetransmitter, thereby setting the modem 5 to the transmission mode. Thesignal is also used to initiate the transmitter 51. The MAC control unit30 directs the busy tone transmission unit 34 to start to transmit a bitstream including a predetermined iterative bit pattern for busy tones tothe modulator 52 in the modem 5. The modulator 52 modulates the receivedbit stream in accordance with the frequency band and the modulationscheme for the busy tone channel, and starts to transmit it on the busytone channel through the transmitter 51 (step S12).

Directing the MAC control unit 30 to start a busy tone transmission, theCPU 0 updates the connection information on the connection control tablewith the contents indicating the connection establishment state (stepS13). Thus, the connection has been established.

Then, the CPU 0 generates a DATA frame smaller than the maximum sizeheld in the connection control table from data on the memory 1, andsends the DATA frame on the data channel (step S14).

To be more specific, the CPU 0 generates a common header of a DATA frame(hereinafter DATA header) from the connection control table. The typefield in the DATA header has an identification of the type of DATA. Thedestination address field has the address of the receiving station inthe connection control table. The source address field has the addressof the apparatus. The sequence number field has the CSEG of theconnection control table. Then, the CPU 0 takes out data held in thememory 1, deducting the total length for the preamble, start delimiter,common header, CRC code, and end delimiter from the maximum frame lengthon the connection control table, and links the taken data to the end ofthe DATA header as a data part. When the data part includes the end bitof the data held on the memory 1, the EOP bit of the type field is setto 1, and otherwise it is set to 0. The DATA header linked with a datapart is called a partial DATA frame hereinafter. The partial DATA frame,which is obtained by deducting the preamble, start delimiter, CRC, andend delimiter from the DATA frame, is a main part of a DATA frame. TheCPU 0 stores a partial DATA frame thus generated to a predetermined areain the memory 1. The partial DATA frame is kept for retransmission evenafter it has been transmitted on the data channel until an ACK frame toconfirm the DATA frame is received.

Then, the CPU 0 directs the MAC control unit 30 to transmit a DATAframe, and further directs the DMA controller 2 to start thetransmission of the partial DATA frame on the memory 1 to the FIFO 32.The transmission is performed in the same manner as the transmission ofthe RCON header explained in step S03.

The MAC control unit 30 sends a signal to the signal conductor 302 toswitch the Rx/Tx switch 40 in the modem 4 to the transmitter, settingthe modem 4 to the transmission mode. The signal is also used toinitiate the transmitter 41. The MAC control unit 30 directs the datatransmission unit 36 and the FIFO 32 to start a frame transmission.Then, the data transmission unit 36 converts a data stream composed of apartial DATA frame, a preamble, and start delimiter into a bit streamfor the transmission path, starting to transmit it to the modulator 42in the modem 4. The data transmission unit 36 calculates a CRC codeduring the transmission of the bit stream. After the transmission of thepartial DATA frame, the data transmission unit 36 adds the calculatedCRC code and end delimiter to the end of the partial DATA frame, andsends it to the modulator 42 in the form of a bit stream for thetransmission path. The modulator 42 modulates a carrier wave for thetransmitted bit stream in accordance with the frequency band andmodulation method for the data channel, and transmits its bit stream onthe data channel via the transmitter 41, the duplexer 7, and the antenna8.

Completing the transmission of the end delimiter, the data transmissionunit 36 reports this to the MAC control unit 30. The MAC control unit 30waits until the modem 4 completes the transmission of the DATA frame,then switches the Rx/Tx switch 40 to the receiver by sending a signal tothe signal conductor 302, setting the modem 4 to the reception mode. Thesignal is also used to initiate the receiver 43. Then, the MAC controlunit 30 informs the CPU 0 of the completion of the DATA frametransmission.

Informed of the completion of the DATA frame transmission, the CPU 0starts the ACK wait timer, with 0 as the initial value (step S15).

When a signal on the data channel has been sent to the receiver 43 inthe modem 4 and further to the data reception unit 35 in the form of abit stream through the demodulator 44, the data reception unit 35 findsout the bit pattern of the start delimiter from the bit stream, andregards the bits following the start delimiter as a frame. Recognizingthat the frame is destined for the apparatus, the data reception unit 35reports it to the MAC control unit 30, and starts to store the receivedframe to the FIFO 31 for reception. Prior to the frame storage to theFIFO 31, the MAC control unit 30 sends a control signal to the FIFO 31to enable the writing of data from the data reception unit 35. The datareception unit 35 examines the CRC in the same manner as the reception aCCON frame in step S09. When a CRC error has been detected, it isprocessed in the same manner as explained in the reception of a CCONframe.

In response to the start of storing a data stream to the FIFO 31 forreception, the DMA controller 2 starts to transfer a frame stored in theFIFO 31 to the memory 1 in the same manner as explained in the CCONframe transmission in step S09. If the DMA controller 2 makes aninterruption to the CPU 0 to report the completion of the frame storage,and there is no CRC error, then the CPU 0 checks the type field of theframe to determine whether the frame is an ACK frame (step S16). If itis an ACK frame, then the contents of the source address field and thesequence number field are compared with the address of the destinationstation and .CSEQ in the connection control table (step S17). When theyagree, the CPU 0 stops the ACK wait timer (step S18), and increments thevalue of CSEQ on the connection control table by one (step S19).Furthermore, the CPU 0 releases the area in the memory 1 where DATAframes which are held for retransmission is stored (step S20).

The CPU 0 checks the EOP bit of the received ACK frame (step S21), andwhen the bit has a 0 value, the operation goes back to step S14 totransmit the rest of the data.

When the bit has a 1 value, the CPU 0 considers that all the data to betransmitted in the memory 1 have been. successfully received by thedestination station, and directs the MAC control unit 30 to terminatethe busy tone transmission. The MAC control unit 30 directs the busytone transmission unit 34 to stop the busy tone transmission (step S22).Then the MAC control unit 30 sends a signal to the signal conductor 303to switch the Rx/Tx switch 50 in the modem 5 to the receiver, therebysetting the modem 5 to the receptions mode. This signal is also used toinitiate the receiver 53. The MAC control unit 30 reports the completionof the busy tone transmission to the CPU 0. After the completion of thebusy tone transmission, the CPU 0 clears the contents of the connectioncontrol table (step S23), and returns to the start.

Recognizing the reception of an RCON frame destined for the apparatus onthe busy tone channel (step S051) in the same manner as explained in thereception of the CCON frame in step S09 before a gap is detected in stepS05, the CPU 0 clears the connection control table (step S052) andproceeds to step R01 to carry out a data reception process which will bedescribed below. Until an RCON frame is received, the CPU 0 continues toobserve the busy tone channel back in the step S04.

If the value of the CCON wait timer has reached the maximum wait timefor the connection establishment confirmation without the reception of aCCON frame on the busy tone channel in the step S09 (step S091), the CPU0 updates the number of times of RCON frame retransmission on theconnection control table by adding one (step S092). Then, the CPU 0checks whether the number of times of the RCON frame retransmission. hasreached the predetermined maximum number of times for the connectionestablishment request (step S093). If it has reached the number, theoperation goes to step S23 to clear the connection control table, andreturns to the start of the operation. If it has not reached the number,the CPU 0 put the connection information on the connection control tableback to the RCON frame transmission wait state (step S094), and returnsto the step S03 to retransmit an RCON frame including an RCON headerheld in the memory 1 for retransmission.

(Data Reception Operations)

Operations for data reception of the radio communication apparatus ofthe present embodiment is described as follows with reference to theFIG. 9.

Recognizing the reception of an RCON frame on the busy tone channel(step R) in the same manner as explained in the reception of the CCONframe in step S09, the CPU 0 generates a connection control table andstores it in a predetermined area in the memory 1 (step R01). In thestep R01, the address of the destination station and CSEQ on theconnection control table are respectively set to the contents of thedestination address field and the sequence number field of the receivedRCON frame. The numbers of times of RCON frame retransmission and DATAframe retransmission are set to any values, and the connection state isset to the CCON transmission wait state.

Then, the CPU 0 generates a common header of a CCON frame (hereinafterCCON header) and stores it in a predetermined area in the memory 1 (stepR02).

The type field in the CCON header has an identification of the type ofCCON frame. The destination address field and the sequence number fieldrespectively have the address of the destination station and CSEQ on theconnection control table. The source address field has the address ofthe apparatus. The CPU 0 transfers the generated CCON header to the FIFO32 in the same manner as explained in the step S03 (step R03), and atthe same time, directs the MAC control unit 30 to start a CCCON frametransmission. Furthermore, the CPU 0 initiates the gap wait timer withan initial value 0 (step R04).

The MAC control unit 30 starts to observe the busy tone channel in thesame manner as in the steps S04 and S05 (step R05), to determine whethera gap has been detected from the busy tone channel (step R06).

In the case where a gap has been detected, a CCON frame is generatedfrom the CCON header in the FIFO 32, and transmitted on the busy tonechannel (step R07).

Completing the transmission of the end delimiter of the CCON frame, thebusy tone transmission unit 34 reports it to the MAC control unit 30.The MAC control unit 30 waits until the modem 5 completes thetransmission of the CCON frame, then switches the Rx/Tx switch 50 to thereceiver by sending a signal to the signal conductor 303, setting themodem 5 to the reception mode. The signal is also used to initiate thereceiver 53. Then, the MAC control unit 30 informs the CPU 0 of thecompletion of the CCON frame transmission. Receiving the information,the CPU 0 stops the gap wait timer (step R08).

The CPU 0 waits for an estimated propagation delay of the CCON frame, tobe caused between the apparatus and the destination terminal (step R09),and directs the MAC control unit 30 to start the busy tone transmission,which is started in the same manner as in the step S12 (step R10). Then,the CPU 0 changes the connection state on the connection control tableto the connection establishment state (step R11), to initiate theconnection holding timer with an initial value 0 (step R12).

When a frame on the data channel destined for the apparatus has beenstored in the memory 1 in the same manner as an ACK frame is received inthe step S16, the CPU 0 determines whether it is a DATA frame or not bychecking the type field (step R13). If it is a DATA frame, then the CPU0 compares the contents of the source address field with the address ofthe destination terminal on the connection control table (step R14). Ifthey agree, the CPU 0 further compares the contents of the sequencenumber field (hereinafter RSEQ) with the CSEQ on the connection controltable. If the RSEQ and the CSEQ agree (step R15), then the data part inthe received DATA frame is taken out and stored in the predeterminedarea (step R16). The CPU 0 further increments the CSEQ on the connectioncontrol table by one (step R17).

Then, an ACK frame, which confirms the reception of the DATA frame isgenerated and transmitted in the same manner as the generation and thetransmission of a DATA frame in the step S14 (step R18). The address ofthe destination terminal and RSEQ on the connection control table arerespectively written into the destination address field and the sequencenumber field of the ACK frame being transmitted. The EOP bit of thereceived DATA frame is written on the EOP bit of the ACK frame. Thecompletion of the ACK frame transmission is reported to the CPU 0through the data transmission unit 36 and the MAC control unit 30 in thesame manner as in the step S14.

In response to the report, the CPU 0 initiates the connection holdingtimer again with an initial value 0 (step R19).

The CPU 0 checks the EOP bit of the received DATA frame (step R20), andin the case that the value is 0, goes back to the step R13 to wait forthe reception of a DATA frame from the destination station. In the casethat the EOP bit has a 1 value, the CPU 0 waits until the connectionhold timer reaches a predetermined maximum connection hold time (stepR21), and terminates the busy tone transmission in the same manner asexplained in the step S22 (step R22). Being informed of the completionof the busy tone transmission through the busy tone transmission unit 34and the MAC control unit 30, the CPU 0 clears the connection controltable (step R23) and returns to the start. If the gap wait timer hasreached its maximum without the detection of a gap in the step R09 (stepR061), the operation proceeds to the step R23 to release the connectioncontrol table and returns to the start.

If the connection holding timer has reached the predetermined maximumconnection hold time without the reception of a DATA frame in the stepR13 (step R131), the CPU 0 proceeds to step R22 to terminate the busytone transmission, regarding the connection as being disconnected. Then,the CPU clears the connection control table and goes back to the start.

When the RSEQ and the CSEQ do not agree in the step Rl5, the receivedDATA frame is abandoned (step R151). When t:e RSEQ is smaller than theCSEQ (step R152), it is regarded as double reception, and the operationproceeds to step R18, skipping to take out a data part or to update theCSEQ. In the step R18, an. ACK frame. to confirm the DATA frame isgenerated and transmitted to perform the subsequent process.

When the RSEQ is larger than the CSEQ, it is regarded as an abnormalframe, and the operation directly goes back to step R13.

Before the connection is released in the step R21, if a DATA frame isreceived from the destination terminal while the CPU 0 is waiting theconnection hold timer to reach its maximum (step R211), the CPU 0generates and transmits the ACK frame to confirm the DATA frame (stepR212), initiates the connection hold timer again (step R213), and goesback to step R21.

(Effects)

As apparent from the explanation hereinbefore, according to the radiocommunication apparatus of the present embodiment;, both thetransmitting terminal and the receiving terminal are transmitting a busytone on the busy tone channel when they are n data communication.Another terminal which is ready to start transmission must confirm thatthere is no busy tone on the busy tone channel. Consequently, all theterminals in the communication range of these transmitting and receivingterminals know that these two are in communication, so that they do notdisturb it. The HTP is avoided in such a manner according to the radiocommunication apparatus of the present embodiment.

Furthermore, two terminals within a certain communication range canestablish a connection and exchange data without a third terminal suchas a base station, so that a distributed environment can be realized.

Furthermore, the entire network is prevented from becoming unable tocommunicate due to a failure of the base station.

Once a connection has been established between a transmitting terminaland a receiving terminal, all the data frames constituting a data packetare repeatedly transmitted. While the data frames are being repeatedlytransmitted, busy tones are transmitted continuously, so that the datacommunication between the two terminals is not disturbed box otherterminals. Consequently, the radio communication apparatus of thepresent embodiment has data transmission with higher efficiency thanother systems that demand a connection establishment for each dataframe.

FIG. 10 is a graph showing the results of a numerical simulation of thethroughput property of the radio communication apparatus of the presentembodiment together with the results of CSMA/CA+Ack system forcomparison.

According to the simulation, a 1500 byte data packet is sent as 128 bytedata frames, and the network is composed of 9 terminals: A1-A3, B1-B3,and C1-C3. The 9 terminals are divided into 3 sub groups: A, B, and C,and communications are carried out within each sub group. However, eachterminal sometimes receives a frame transmitted from another sub group,causing a frame collision. The maximum confirmation wait time is set tobe 1.2 times of the sum of a data frame propagation delay and aconfirmation frame propagation delay. The data frames which have notbeen confirmed by the acknowledgement frame is retransmitted 5 times atmost. If at least one of the data frames constituting a data packet hasfailed to reached the destination station, it is considered that thetransmission of the entire data packet has been unsuccessful.

The presence and absence of HTP are expressed by using two types ofaverage path loss, assuming that the path loss between two terminalsobeys a Rayleigh fading. The average path loss in the case that HTP ispresent is shown in FIG. 11, and the average path loss in the case thatHTP is absent is fixed to 87 dB. When the path loss is over 115 dB, aframe is assumed to be dropped.

In FIG. 10, the horizontal axis indicates the total load of all theterminals normalized at a transmission rate unique to the data channel.The total load is one of the parameters for the simulation, andindicates a degree of the data transmission congestion in the entirenetwork. The vertical axis indicates the total throughput (normalizedthroughput) of all the terminals normalized with the total load. Thenormalized throughput is obtained from the simulation and represents therate of successful data transmission.

As shown in FIG. 10, the radio communication method of the presentinvention can produce higher throughput, and is less affected by the HTPthan the CSMA/CA+Ack scheme. As a result, higher efficiency of datatransmission can be realized.

<Embodiment 2>

The second embodiment of the present invention will be describedhereinafter in which the like components are labeled with like referencenumerals with respect to the first embodiment, and the description ofthese components is not repeated. The busy tone channel and the datachannel are assigned different frequency bands from each other just likein the first embodiment.

The present embodiment is different from the first embodiment in that adata channel is used for a connection establishment with an RCON frameand a CCON frame, instead of a busy tone channel.

(The Entire Construction of the Radio Communication Apparatus)

The radio communication apparatus of the present embodiment has the samefundamental construction as the first embodiment shown in FIG. 4;however, the MAC unit 3 and the modem 5 for the busy tone channel areconstructed differently from their equivalents in the first embodimentshown in FIGS. 5 and 6. The frames used in this embodiment are equal tothose used in the first embodiment shown in FIGS. 3A-3E; however RCONframes and CCON frames to be transmitted on the busy tone channel in thefirst embodiment are transmitted on the data channel.

(The Construction of the MAC Unit 3)

FIG. 12 is a block diagram showing the construction of the MAC unit 3 ofthis embodiment. FIG. 12 is different from FIG. 5 showing theconstruction of the MAC unit 3 of the first embodiment in that there areno busy tone reception unit 33 and no data line extending from the FIFO32 to the busy tone transmission unit 34. The busy tone transmissionunit 34 of this embodiment transmits busy tones only, and the RCONframes and the CCON frames are transmitted by the data transmission unit36.

(The Construction of the Modem 5)

FIG. 13 is a block diagram showing the construction of the modem 5 forthe busy tone channel of the radio communication apparatus of thisembodiment. FIG. 13 is different from FIG. 6B showing the constructionof the modem 5 of the first embodiment in that there is no demodulator54 provided.

(Operations of the Entire Radio Communication Apparatus)

FIGS. 14-16 are flowcharts depicting operations of the radiocommunication apparatus of this embodiment, which respectivelycorrespond to FIGS. 7-9 of the first embodiment. FIG. 14 shows theoverall operation of the radio communication apparatus, FIG. 15 showsthe data transmission operation, and FIG. 16 shows the data receptionoperation. The same operations as the first embodiment are notexplained.

In the flowchart of FIG. 14, the radio communication apparatus performsa data reception subroutine when received an RCON frame destined for theapparatus (step R). After the completion of the data reception, theoperation goes back to step R.

In the case that the apparatus has not received an RCON frame destinedfor the apparatus (step R), it determines whether there are data to betransmitted in the memory 1 (step S). When there are such data, theapparatus performs a data transmission subroutine, and after thecompletion of data transmission, returns to the step R. In contrast,when there are no data to be transmitted, the apparatus directly returnsto the step R.

As will be described below, when an RCON frame destined for theapparatus has been received on the busy tone channel at an early stageof the connection establishment process, a data reception process hasprecedence over the data transmission process.

(Data Transmission Operations)

The operations for data transmission are explained hereafter withreference to FIG. 15. The operations up to step S05 in FIG. 15 areincluded in FIG. 8 for the first embodiment, so that they are notdetailed again.

Responding to the detection of the presence of a gap on the busy tonechannel at step S05, the MAC control unit 30 switches the Rx/Tx switch40 in the modem 4 to the transmitter by sending a signal to the signalconductor 302, setting the modem 4 to the transmission mode. The signalis also used to initiate the transmitter 41. The MAC control unit 30directs the data transmission unit 36 and the FIFO 32 to transmit aframe. The data transmission unit 36 generates a data stream including apreamble and a start delimiter at the head of an RCON header in the FIFO32, and converts the data stream into a bit stream for the transmissionpath, and starts to transmit it to the modulator 42 of the modem 4 forthe data channel. The data transmission unit 36 calculates CRC duringthe transmission of the bit stream. When the RCON header in the FIFO 32has been transmitted, the data transmission unit 36 adds the calculatedCRC and the end delimiter to the end of the RCON header, converts itinto a bit stream for the transmission path, and transmits it to the.modulator 42. The modulator 42 modulates a carrier wave for thetransmitted bit stream and transmits the bit stream onto the datachannel through the transmitter 41, duplexer 7, and antenna 8. Thus, thetransmission of the RCON frame is started (step S06).

Having completed the transmission of the end delimiter of the RCON frameto the modulator 42, the data transmission unit 36 reports it to the MACcontrol unit 30. The MAC control unit 30 waits until the modem 4completes the transmission of the RCON frame, then switches the Rx/Txswitch 40 to the receiver, by sending a signal to the signal conductor302. As a result, the modem 4 for the data channel is set to thereception mode. This signal is also used to initiate the receiver 43.Then, the MAC control unit 30 informs the CPU 0 of the completion of theRCON frame transmission. The CPU 0 changes the connection state of theconnection control table in the memory 1 to the CCON reception waitstate (Step S07). Then, the CPU 0 initiates the CCON wait timer with 0as the initial value (step S08).

When a signal on the data channel is received by the receiver 43 in themodem 4 and sent to the data reception unit 35 through the demodulator44 in the form of a bit stream, the data reception unit 35 finds out thebit pattern of the start delimiter from the bit stream, and regards thebits following the start delimiter as a frame. Recognizing that theframe is destined for the apparatus, the data reception unit 35 reportsit to the MAC control unit 30, and converts the received frame from thebit stream for the transmission path into a data stream until the enddelimiter is detected, storing to the FIFO 31 for reception. The enddelimiter is not stored to the FIFO 31. The data reception unit 35examines the CRC of the frame. Prior to the frame storage to the FIFO31, the MAC control unit 30 sends a control signal to the FIFO 31 toenable the writing of data from the data reception unit 35.

Then, it is determined whether the frame received by the CPU 0 is a CCONframe in step S09 along with the same operation shown in FIG. 8 for. thefirst embodiment. The operations from step S10 to step S23 are performedin the same manner as in the first embodiment.

If the CPU 0 has recognized the reception of an RCON frame destined forthe apparatus (step S051) before a gap is detected in step S05 in thesame manner as explained in the CCON frame reception in step S09, theradio communication apparatus of this embodiment performs the operationson and after the step S052, which are equal to their equivalents in FIG.8 for the first embodiment.

If the value of the CCON wait timer has reached the predeterminedmaximum wait time for the connection establishment confirmation withoutthe reception of a CCON frame on the data channel in the step 509 (stepS091), the radio communication apparatus of this embodiment performs theoperations on and after the step S092, which are equal to theirequivalents in FIG. 8 for the first embodiment.

The operations from step S161 to step S164 are also equal to theirequivalents in FIG. 8.

(Data Reception Operations)

The operations for data reception are explained hereafter with referenceto FIG. 16.

Recognizing the reception of an RCON frame on the data channel (step R)in the same manner as explained in the CCON frame reception in step S09in FIG. 15, the CPU 0 performs the operations on and after the step R01.The operations from step R01 to step R06 are equal to their equivalentsin FIG. 9 for the first embodiment.

In the case where a gap has been detected on the busy tone channel instep R06, a CCON frame is generated from the CCON header in the FIFO 32for transmission, and transmitted on the data channel (step R07).

Completing the transmission of the end delimiter of the CCON frame, thedata transmission unit 36 reports it to the MAC control unit 30. The MACcontrol unit 30 waits until the modem 4 completes the transmission ofthe CCON frame, then switches the Rx/Tx switch 40 to the receiver bysending a signal to the signal conductor 302, setting the modem 4 to thereception mode. The signal is also used to initiate the receiver 43.Then, the MAC control unit 30 informs the CPU 0 of the completion of theCCON frame transmission. Receiving the information, the CPU 0 stops thegap wait timer (step R08).

Then, the operations from step R09 to step R23 are performed in the samemanner as explained in FIG. 9 for the first embodiment.

The operations in the cases where the gap wait timer has reached itsmaximum without the detection of a gap on the busy tone channel in thestep R061, where the connection hold timer has reached its maximum timewithout the reception of a DATA frame in the step R131, and where RSEQand CSEQ do not agree to each other in the steps R151 and R152 are equalto the respective operations in the first embodiment.

Furthermore, the operations from the step R211 to step R213 are equal totheir equivalents in the first embodiment.

(Effects)

As apparent from the explanation hereinbefore, the radio communicationapparatus of this embodiment produces the same effects as those of thefirst embodiment. In other words, HTP can be solved because both thetransmitting terminal and the receiving terminal transmit a busy tone onthe busy tone channel when they are in data communication.

Furthermore, two terminals within a certain communication range canestablish a connection and exchange data without a third terminal suchas a base station, so that a distributed environment can be realized.

Furthermore, the entire network is prevented from becoming unable tocommunicate due to a failure of the base station.

Since the controlling procedure in data transmission is performed in thesame manner as in the first embodiment, effective data transmission canbe realized.

The radio communication apparatus of this embodiment has another effectwhich can not be obtained from the first embodiment. Since frames forconnection establishment are transmitted by means of the data channel,the busy tone channel is used exclusively to transmit busy tones.Consequently, the band width of the busy tone channel can be smallerthan in the first embodiment, contributing the effective use of thefrequency band.

<Embodiment 3>

The third embodiment of the present invention will be describedhereinafter in which the like components are labeled with like referencenumerals with respect to the first and second embodiments, and thedescription of these components is not repeated. The busy tone channeland the data channel are assigned different frequency bands from eachother just like in the first and second embodiments.

The present embodiment is different from the first embodiment in thatthe data channel is used for connection establishment, instead of thebusy tone channel, and different from the second embodiment in that busytones are transmitted while an RCON frame and a CCON frame are inprocess of transmission.

(The Overall Construction of the Radio Communication Apparatus)

The radio communication apparatus of this embodiment has the samefundamental construction as that of the first embodiment shown in FIG.4. The MAC unit 3 of the present embodiment has the same construction asthat of the second embodiment shown in FIG. 12. The frames of thisembodiment are the same as those of the first embodiment shown in FIG.3; however RCON frames and CCON frames to be transmitted on thE busytone channel in the first embodiment are transmitted on the datachannel.

(Operations of the Entire Radio Communication Apparatus)

The operations of the entire radio communication apparatus of thepresent embodiment are the same as those of the second embodiment shownin FIG. 14 except for the contents of the data transmission subroutineand the data reception subroutine.

(Data Transmission Operations)

The operations for data transmission of this embodiment differs fromthose of the second embodiment only in the RCON frame transmissionoperation.

FIG. 17 is a flowchart depicting the RCON frame transmission operationof this embodiment, which corresponds to the step S06 of FIG. 15 whichshows the RCON frame transmission operation of the second embodiment.

In FIG. 17, having detected a gap in the busy tone channel (step S05 inFIG. 15), the MAC control unit 30 switches the Rx/Tx switch 40 in themodem 4 and the Rx/Tx switch 50 in the modem 5 to the transmitter bysending signals to the signal conductors 302 and 303, setting the modems4 and 5 to the transmission mode (step S301). These signals are alsoused to initiate the transmitters 41 and 51 respectively. Then, the MACcontrol unit 30 directs the busy tone transmission unit 34 to start busytone transmission.

In response to the direction of the MAC control unit 30, the busy tonetransmission unit 34 starts to transmit a bit stream including apredetermined iterative bit pattern for busy tones to the modulator 52in the modem 5. The modulator 52 modulates a carrier wave for thetransmitted bit stream in accordance with the frequency band andmodulation scheme for the busy tone channel, and starts to transmit iton the busy tone channel through the transmitter 51, the duplexer 7, andthe antenna 8 (step S302).

Then, the MAC control unit 30 directs the data transmission unit 36 andthe FIFO 32 to transmit a frame. The data transmission unit 36 generatesa data stream including a preamble and a start delimiter at the head ofan RCON header in the FIFO 32, converts the data stream into a bitstream for the transmission path, and starts to transmit it to themodulator 42 of the modem 4 for the busy tone channel. The modulator 42modulates a carrier wave for the transmitted bit; stream and transmitsthe bit stream on the data channel through the transmitter 41, duplexer7, and antenna 8 (step S303).

The data transmission unit 36 calculates CRC during the transmission ofthe bit stream to the modulator 42. After the transmission of the RCONheader stored in FIFO 32, the data transmission unit 36 adds thecalculated CRC and end delimiter to the end of the RCON header, andsends it to the modulator 42 in the form of a bit stream for thetransmission path.

Having completing the transmission of the end delimiter of the RCONframe to the modulator 42 (step S304), the data transmission unit 36reports it to the MAC control unit 30. The MAC control unit 30 waitsuntil the modem 5 completes the transmission of the RCON frame, thendirects the busy tone transmission unit 34 to stop the busy tonetransmission (step S305).

The MAC control unit 30 then switches the Rx/Tx switches 40 and 50 tothe receiver by sending signals to the signal conductors 302 and 303,setting the modems 4 and 5 to the reception mode (step S306). Thesesignals are also used to initiate the receivers 43 and 53 respectively.Then, the MAC control unit 30 informs the CPU 0 of the completion of theRCON frame transmission. The subsequent operations are equal to theoperations on and after the step S07 in FIG. 15.

(Data Reception Operations)

The operations for data reception of this embodiment are explainedhereafter. The operations differs from those of the second embodimentonly in operations from a CCON frame transmission through a busy tonetransmission which correspond to step R07 through step R10 in FIG. 16.

FIG. 18 is a flowchart depicting a CCON frame transmission and a busytone transmission of this embodiment, which corresponds to the steps R07through R10 of FIG. 16 for the second embodiment.

In FIG. 18, having detected a gap on the busy tone channel (step R06 inFIG. .16), the MAC control unit 30 switches the Rx/Tx switch 40 in themodem 4 and the Rx/Tx switch 50 in the modem 5 to the transmitter bysending signals to the signal conductors 302 and 303, setting the modems4 and 5 to the transmission mode (step R301). These signals are alsoused to initiate the transmitters 41 and 51 respectively.

Then, the MAC control unit 30 directs the busy tone transmission unit 34to start busy tone transmission. In response to the direction of the MACcontrol unit 30, the busy tone transmission unit 34 starts to transmit abit stream including a predetermined iterative bit pattern for busytones to the modulator 52 in the modem 5. The modulator 52 modulates acarrier wave for the transmitted bit stream in accordance with thefrequency band and modulation scheme for the busy tone channel, andstarts to transmit it on the busy tone channel through the transmitter51, the duplexer 7, and the antenna 8 (step R302).

Then, the MAC control unit 30 directs the data transmission unit 36 andthe FIFO 32 to transmit a frame. The data transmission unit 36 generatesa data stream including a preamble and a start delimiter at the head ofan RCON header in the FIFO 32, converts the data stream into a bitstream for the transmission path, and starts to transmit it to themodulator 42 of the modem 4 for the busy tone channel. The modulator 42modulates a carrier wave for the transmitted bit stream and transmitsthe bit stream on the data channel through the transmitter 41, duplexer7, and antenna 8 (step R303).

The data transmission unit 36 calculates CRC during the transmission ofthe bit stream to the modulator 42. After the transmission of the CCONheader stored in FIFO 32, the data transmission unit 36 adds thecalculated CRC and end delimiter to the end of the CCON header, andsends it to the modulator 42 in the form of a bit stream for thetransmission path.

Having completed the transmission of the end delimiter of the CCON frameto the modulator 42 (step R304), the data transmission unit 36 reportsit to the MAC control unit 30. The MAC control unit 30 waits until thetransmission of the RCON frame is completed, switches the Rx/Tx switch40 to the receiver by sending a signal to the signal conductor 302,setting the modem 4 to the reception mode (step R305). The signal isalso used to initiate the receiver 43. Then, the MAC control unit 30informs the CPU 0 of the completion of the CCON frame transmission.Being informed of the completion, the CPU 0 stops the gap wait timer(step R306). The subsequent operations are equal to the operations onand after the step R11 in FIG. 16.

(Effects)

As apparent from the explanation hereinbefore, the radio communicationapparatus of this embodiment produces the same effects as those of thefirst and second embodiments. In other words, HTP can be solved becauseboth a transmitting terminal and a receiving terminal transmit a busytone on the busy tone channel when they are in data communication.

Furthermore, two terminals within a certain communication range canestablish a connection and exchange data without a third terminal suchas a base station, so that a distributed environment can be realized.

Since the controlling procedure in data transmission is performed in thesame manner as in the first embodiment, effective data transmission canbe realized.

The busy tone channel is used exclusively to transmit busy tones whichindicate that data are in process of transmission, so that the bandwidth of the busy tone channel can be smaller than in the firstembodiment, contributing the effective use of the frequency band.

The radio communication apparatus of this embodiment has another effectwhich can not be obtained from the first and second embodiments asfollows.

According to the first and second embodiments, a busy tone is nottransmitted while an RCON (CCON) frame is in process of transmission. Asa result, when two terminals are in data communication, a third terminalmay start a transmission, to disturb their data communication. This canbe avoided if an RCON (CCON) frame is transmitted only in a case where agap on the data channel has been detected in the same manner as a gap isdetected on a busy tone channel, prior to the transmission. However,these two different gap detections make the process complicated and thecircuit enlarged.

In contrast, according to the present embodiment, a busy tone istransmitted prior to the transmission of an RCON (CCON) frame, acollision of RCON (CCON) frames can be avoided only by checking the busytone channel. Thus, two terminals can establish a connection in ashorter time because they are less affected by other terminals.

(Supplement)

(1) Although the busy tone channel and the data channel are assigneddifferent frequency bands from each other in the first, second, andthird embodiments, it is possible to use physically the same frequencyband by means of time sharing or code division.

For example, the same frequency band is logically used for two channelsby means of time sharing, each duplexer is operated as an antennaswitch. The duplexers at all the terminals in a radio network switchbetween the busy tone channel and the data channel at every breakpointof time sharing, thereby realizing two logical channels.

In the case where the same frequency band is logically used for twochannels by means of code division, the modems for the busy tone channeland the data channel, which correspond to spread spectrummodulation/demodulation use a carrier having the same frequency. Thelogical two channels are realized by differentiating the spreadingcodes.

Thus, time sharing or code division can contribute to the effective useof the frequency band.

(2) Although the gap times are predetermined in the first, second, andthird embodiment, they can be randomized.

(3) If a terminal which is ready to transmit an RCON frame has receivedan RCON frame destined for the terminal itself while it is observing thebusy tone channel, the terminal is supposed to clear the connectioncontrol table and to receive data in the first, second, and thirdembodiments. However, the data transmission operation can be continued,ignoring the received RCON frame.

In addition, when a signal having more strength than predetermined hasbeen detected while the busy tone channel is being observed, before anRCON (or CCON) frame is transmitted, the busy tone observation may beinterrupted for either a predetermined or randomized time period. Thiscan reduce the power consumption.

(4) A terminal which has received a DATA frame whose EOP bit is 1completes the transmission of a busy tone after it waits until themaximum connection holding time is over, with the use of the connectionholding timer, thereby releasing the connection in the first, second,and third embodiments. However, the wait time is not necessarily limitedto the maximum connection holding time. The subsequent process may bestarted after a wait time which is either shorter or longer than themaximum connection holding time, by using another timer. After a longerwait time, data retransmission in an upper layer level which is causedby the dropping of a ACK frame for the last DATA frame can be prevented.After a shorter wait time, a connection can be released faster, and as aresult, another terminal can start data transmission earlier.

(5) Although a receiving terminal returns an ACK frame every time itreceives a DATA frame in the first, second, and third embodiments, it isnot the only way. A transmitting terminal may carry information torequest acknowledgement in every predetermined number of DATA frames,and returns an ACK frame for the acknowledgement of all the DATA framesthat have not been acknowledged so far only in the case where thereceiving terminal has received a DATA frame including the informationto request acknowledgement. However, if it is necessary to retransmitthe DATA frame in this case, all the DATA frames which have not beenacknowledged by an ACK frame must be retransmitted. For another method,it is possible that no ACK frames are transmitted at all. In this case,retransmitting operations are up to an upper layer level.

(6) Both a transmitting terminal and a receiving terminal continue totransmit a busy tone when a connection is being established in thefirst, second, and third embodiments; however, the busy tone may betransmitted intermittently. In that case, it is necessary that theintermitting time period is below a predetermined gap time. This canreduce the power consumption.

(7) Although a receiving terminal transmits a busy tone after thecompletion of a CCON frame transmission in the second embodiment, a busytone may be transmitted at the same time as the start of the CCON frametransmission. This makes the second embodiment realize a function ofavoiding a collision of CCON frames in the same manner as the thirdembodiment.

(8) In the third embodiment, a transmitting terminal continuouslytransmits a busy tone while it is transmitting an RCON frame; however,the transmission of the busy tone may be stopped when a certain time haspassed after the start of the RCON frame transmission. This can reducethe power consumption.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless such changes and modifications depart fromthe scope of the present invention, they should be construed as beingincluded therein.

What is claimed is:
 1. A radio communication method for transmitting andreceiving data between a first terminal and a second terminal using acontrol channel and a data channel, said method comprising the stepsof:a connection establishment phase which includes:a first check step inwhich the first terminal checks whether a busy tone, a first controlsignal, and a second control signal are all absent on the controlchannel, wherein the first control signal conveys a connection requestand the second control signal conveys an acknowledgment of theconnection request; a connection request step in which the firstterminal transmits the first control signal to the second terminal viathe control channel when the first terminal confirms that the busy tone,the first control signal, and the second control signal are all absenton the control channel; a second check step in which the secondterminal, on receiving the first control signal from the first terminal,checks whether the busy tone, the first control signal, and the secondcontrol signal are all absent on the control channel; a connectionacknowledgment step in which the second terminal transmits the secondcontrol signal to the first terminal via the control channel when thesecond terminal confirms that the busy tone, the first control signal,and the second control signal are all absent on the control channel,then starts continuously transmitting the busy tone to the controlchannel; and a busy tone transmission step in which the first terminal,on receiving the second control signal from the second terminal, startscontinuously transmitting the busy tone to the control channel; and adata communication phase which includes:a data communication step inwhich a data communication between the first terminal and the secondterminal via the data channel starts; and a data communication end stepin which the data communication between the first terminal and thesecond terminal ends and the first terminal and the second terminal stoptransmitting the busy tone.
 2. A radio communication method fortransmitting and receiving data between a first terminal and a secondterminal using a control channel and a data channel, said methodcomprising the steps of:a connection establishment phase whichincludes:a first check step in which the first terminal checks whether abusy tone is absent on the control channel; a connection request step inwhich the first terminal transmits a first control signal to the secondterminal via the data channel when the first terminal confirms that thebusy tone is absent on the control channel, wherein the first controlsignal conveys a connection request; a second check step in which thesecond terminal, on receiving the first control signal from the firstterminal, checks whether the busy tone is absent on the control channel;a connection acknowledgment step in which the second terminal transmitsa second control signal to the first terminal via the data channel whenthe second terminal confirms that the busy tone is absent on the controlchannel, wherein the second control signal conveys an acknowledgment ofthe connection request, then starts continuously transmitting the busytone to the control channel; and a busy tone transmission step in whichthe first terminal, on receiving the second control signal from thesecond terminal, starts continuously transmitting the busy tone to thecontrol channel; and a data communication phase which includes:a datacommunication step in which a data communication between the firstterminal and the second terminal via the data channel starts; and a datacommunication end step in which the data communication between the firstterminal and the second terminal ends and the first terminal and thesecond terminal stop transmitting the busy tone.
 3. A radiocommunication apparatus for transmitting and receiving data to and froma desired radio communication apparatus using a control channel and adata channel, said radio communication apparatus comprising:a connectionestablishment means which includes:a connection request unit forchecking whether a busy tone, a first control signal conveying aconnection request, and a second control signal conveying anacknowledgment of the connection request are all absent on the controlchannel, then on confirming an absence of the signals, transmitting thefirst control signal to the desired radio communication apparatus viathe control channel; a connection acknowledgment unit which, onreceiving a first control signal from the desired radio communicationapparatus, checks whether the busy tone, the first control signal, andthe second control signal are all absent on the control channel, then onconfirming an absence of the signals, transmits the second controlsignal to the desired radio communication apparatus via the controlchannel, and starts continuously transmitting the busy tone to thecontrol channel; a busy tone transmission unit which, on receiving asecond control signal from the desired radio communication apparatus,starts continuously transmitting the busy tone to the control channel;and a data communication means which includes:a data communication unitfor performing a data communication using the data channel after eitherof the connection acknowledgment unit and the busy tone transmissionunit starts transmitting the busy tone; a data communication end unitfor ending the data communication and stopping transmitting the busytone.
 4. A radio communication apparatus for transmitting and receivingdata to and from a desired radio communication apparatus using a controlchannel and a data channel, said radio communication apparatuscomprising:a connection establishment means which includes:a connectionrequest unit for checking whether a busy tone is absent on the controlchannel, then on confirming an absence of the busy tone, transmitting afirst control signal conveying a connection request to the desired radiocommunication apparatus via the data channel; a connectionacknowledgment unit which, on receiving a first control signal from thedesired radio communication apparatus, checks whether the busy tone isabsent on the control channel, then on confirming an absence of the busytone, transmits a second control signal conveying an acknowledgment ofthe connection request to the desired radio communication apparatus viathe data channel, and starts continuously transmitting the busy tone tothe control channel; a busy tone transmission unit which, on receiving asecond control signal from the desired radio communication apparatus,starts continuously transmitting the busy tone to the control channel;and a data communication means which includes:a data communication unitfor performing a data communication using the data channel after eitherof the connection acknowledgment unit and the busy tone transmissionunit starts transmitting the busy tone; and a data communication endunit for ending the data communication and stopping transmitting thebusy tone.